The invention relates to a lifting device for lifting an ordered stack of articles, which lifting device is intended for cooperating with an unstacking device and with a stack-feeding conveyor.
The device is particularly intended for an unstacking device in which the articles to be fed are discharged from above. The stacks that are unstacked in the lifting device, are moved to the lifting device by a stack-feeding conveyor
A problem involved in known lifting devices intended for cooperating with an unstacking device is that the unstacking process is interrupted when a complete stach has been unstacked in the lifting device and a new stack is to be fed into the lifting device. In the known devices, during the feed of a complete stack to the lifting device, it is not possible to continue the unstacking process. As a consequence, in the known lifting devices, the discharge of the articles removed from a stack cannot take place in a continuous manner. Such discontinuous discharge of articles is generally undesired.
The object of the invention is to provide a lifting device without the above-mentioned drawbacks.
To this end, the lifting device is characterized by the features of claim 1.
Due to the particular cooperation of the first lifting means and the second lifting means, the uppermost article of a stack located in the lifting device can, when the lifting device cooperates with an unstacking device, in each case be removed from the same place in a continuous manner. In this context, xe2x80x98continuousxe2x80x99 must at least be understood to mean xe2x80x98at a fixed rhythmxe2x80x99. As soon as an article has been removed from the stack, the lifting means will move the stack located in the lifting device slightly upwards, causing a next uppermost article to be located at the fixed, desired level, whence that next article can then be removed again by the unstacking device.
As the lifting device possesses first lifting means and second lifting means, a completely formed stack and a partially formed stack can simultaneously be located in the device. As a result, when the lifting device cooperates with an unstacking device, a second complete stack can be fed to the lifting device and received by the first lifting means, while the second lifting means support an already partially unstacked first stack, so that an uppermost article of this first stack is always kept at the desired fixed level. As soon as the first stack has been unstacked completely, the uppermost article of the second stack is moved to the desired fixed level, so that the unstacking procedure can be continued without interruption. In the meantime, the second lifting means can, after a passage of time, take over the second stack from the first lifting means, after which the first lifting means are moved into a position in which they are ready to receive a third stack.
Summarizing, it can be stated that the presence of the first lifting means and the second lifting means enables a continuous unstacking process, which unstacking process need not be interrupted for feeding or discharging a complete stack of articles. The lifting device according to the invention can be realized in a relatively simple manner and can hence be manufactured in an economical manner. As the lifting frames can be brought from a folded-down position into a folded-up position, the lifting frames can pass an entirely or partially formed stack in vertical direction, which is important for causing the unstacking process to take place in a continuous manner.
In should be noted that from U.S. Pat. No. 2,205,767 a stacking device is known which comprises first and second lifting means. The second lifting means do engage the lower side of the lowermost article of the stack in the same area as the second lifting means. Consequently, the first and second lifting means cannot pass each other. Further, the articles which are supported by the second lifting means have to be removed from the second lifting means by retracting the second lifting means and thereby shifting the stack over the second lifting means.
From U.S. Pat. No. 2,895,624 a stacking device is known for forming a stack of article on a bunk. The known device has first and second lifting elements which engage the lower side of the bunk. The movement and the relative position of the first and second lifting means is coupled by a chain. Consequently, the first lifting means cannot take over a stack from the second lifting means. As a consequence, the supply of articles to the board on which the articles have to be stacked must be interrupted for some time to position an empty bunk while removing a bunk containing a full stack. In view thereof the supply of articles to be stacked cannot be and is not continuous.
Further elaborations of the invention are described in the subclaims and will be specified on the basis of an exemplary embodiment, with reference to the accompanying drawings.